The current GSM/3G and WLAN technologies constitute two separate radio network technologies. They operate at different frequencies and make use of separate designated protocols. Currently standardization work is ongoing on integrating data and other services of WLAN and GSM/3G in the forums of 3GPP, 3GPP2 and IEEE.
Six scenarios dealing with various degrees of integration have been sketched in the third generation partnership project, 3GPP. Scenarios 1, 2 and 3 have been defined so far. However, the work for scenario 6, i.e. WLAN GSM/3G integration of telephony (Circuit Switched voice services) has not yet started.
A desirable concept known as “always best connected” aims to ensure that the best and cheapest service connection is rendered available to the user at all times and performing handover in such a way that the user hardly notices the underlying access technology.
Currently, dual mode mobile phones integrating different kinds of radio access techniques, such as WLAN and GSM/3G, providing prior art access on the choice of the user by means of one apparatus have been rendered available on the marketplace. However, Cellular systems and WLAN systems are currently not interoperable on the network side. If a telephone call is received for a subscriber in GSM/3G, it is not possible to handover the call to a WLAN system, even if the subscriber is in reach of WLAN coverage and is in possession of a dual mode mobile or vice versa. One problem is that there is no integration of WLAN and GSM/3G network nodes or corresponding signaling protocols.
A further problem for the integration of WLAN and GSM/3G services is the pico-cell character of the WLAN radio network. The WLAN radio network consists of a flat structure of pico-cells, not at all suitable for typical mobile user behavior. A telephony call would be difficult to maintain in a WLAN network when a user moves with high speed as he is used to in a cellular network.